The oropharyngeal physiology involved in a normal swallow is an exceedingly complex series of coordinated actions. A host of very different medical conditions, both physical and neurological in nature, can alter normal swallowing. For example, patients suffering stroke, Alzheimer's disease, amyotrophic lateral sclerosis, or traumatic brain injury can exhibit abnormal swallowing. In many instances, the abnormal swallow can and does cause aspiration of food material, both liquids and solids, into the lungs. This is especially prevalent (and life-threatening) in frail patients and in elders. Aspiration of foreign material into the airways leads to increased morbidity in hospitalized patients and can lead to pneumonia. Abnormalities in the human swallow, whether or not the condition results in aspiration of foods, is called dysphagia.
A normal human swallow can be separated into four semi-distinct phases: 1) oral preparation; 2) the oral phase; 3) the pharyngeal phase; and 4) the esophageal phase. Patients who have suffered a stroke, traumatic brain injury, or neuromuscular disorder (such as MS or ALS) have an increased risk of aspiration, and may have difficulty with the oral phase, the pharyngeal phase, or both. Weak or uncoordinated muscle movement when chewing (or in the initial oral phase of swallowing) can cause food to be propelled or fall into the pharynx and into the open airway. This often occurs before the completion of the oral phase of swallowing. Or impaired propulsion can result in residue in the oral cavity, valleculae, or pharynx after the swallow, when the residue may be inhaled into the trachea. Or a delay in the onset of the pharyngeal swallowing response can result in food falling into the airway during the delay when the airway is open. Or reduced peristalsis in the pharynx can leave residue in the pharynx after the swallow is completed that can fall or be inhaled into the airway. Additionally, laryngeal or cricopharyngeal dysfunction can also lead to aspiration because of decreased closure of the airway during swallowing. Any of these conditions, or a combination of these conditions, can lead to aspiration of food or liquids into the airways.
While the standard bedside swallow exam to screen patients is beneficial for evaluating patients at risk for dysphagia, it sheds very little light on the whether the patient is actually aspirating and even less light on the biomechanical etiology of the defect arises. Many patients, due to concomitant neurological defects effecting the sensory response, will silently aspirate, giving no indication (e.g. cough) during the clinical/non-instrumental exam as to their condition. Aspiration in dysphagic patients, however, can be detected using a radiographic modified barium swallow fluoroscopic examination. Videofluoroscopy of the swallow mechanism using barium for its radio-opacity is performed as routine practice to elucidate more clearly the anatomical or neurological deficit causing the dysphagia and the impact of those deficits on bolus transit or flow.
Dynamic fluoroscopic evaluation of the swallow, however, is not without its attendant difficulties and shortcomings. For instance, the imaging compositions conventionally used for fluoroscopic exams are thick suspensions of barium sulfate. Barium is employed because of its large X-ray absorption cross-section, which makes it radio-opaque. The use of barium sulfate suspensions as a radiological contrast medium has a number of drawbacks. A first drawback is that conventional barium sulfate suspensions generally have either poor adhesion to the walls of the oropharynx or too much adhesion. These compositions, having been initially designed to image the gastrointestinal tract, have not been altered much, if any, for use in imaging the mouth and throat. If the walls of the oropharyngeal tract are not sufficiently coated with the contrast agent, an X-ray image cannot be generated; there simply is not enough contrast to visualize the relevant structures. Conversely, if the suspension is made thicker to encourage adhesion, the thick, chalky suspension actually coats the mouth and throat and physically alters the movement of the muscles used for swallowing. Consequently, the image generated is not necessarily indicative of the true swallow response exhibited by the patient. Further, total clearance of material from the oropharyngeal and esophageal cavities would be a useful visual cue to determine whether the function of these structures is within normal limits. If the oropharynx is coated with too much contrast agent, the dense X-ray cross-section creates a complete opacity in the resultant X-ray exposure, which does not provide sufficient detail of the structures involved in swallowing. A complicating factor is the taste and chalky texture of barium suspensions, which makes them generally unpleasant to hold in the mouth and to swallow. Substances that are more food-like in taste and texture would more likely elicit a more representative swallow response.
See, for example, U.S. Pat. No. 4,020,152 to Heitz, which describes barium titanate and barium zirconate X-ray contrast agents. This patent specifically notes that it is quite difficult to generate fluoroscopic images of the oropharyngeal cavity. Heitz states that patients have great difficulty in holding a mouthful of contrast medium at the very back of their throats for a long time without swallowing. When the patient swallows the barium sulfate suspension, it slides over the mucous membranes, often without leaving sufficient contrast agent in place to generate an image. Heitz believes the lack of adhesion is due to the saliva covering the walls of the oropharynx, which substantially reduces the adherence of a barium sulfate suspension. As a result, radiological examination of this key physiological intersection, the junction where aspiration occurs, is difficult and often leads to only mediocre imaging. Failure to generate a clean radiological image of the swallow leads to imprecise diagnosis and treatment.
Moreover, once a patient has been diagnosed as having dysphagia and is known to be aspirating foods, some compensatory treatment must be implemented to prevent further aspiration. One method widely employed is to alter the consistency (i.e., the viscosity) of liquids. Thickened liquids have been shown to inhibit aspiration by increasing bolus transit time, providing more time for airway closure providing greater “mouthfeel” and by providing greater mechanical resistance to the muscles involved in swallowing and to. See, for example, U.S. Pat. No. 5,932,235, to Ninomiya et al.: This patent describes a jellied preparation containing carrageenan, locust bean gum, and a polyacrylic acid. The preparation can be used to thicken liquid foodstuffs.
In hospital, nursing home, and clinical settings, thickened liquids deemed to be “nectar thick” or the more viscous “honey thick”are provided to dysphagic patients. For instance, preferred liquid foods such as milk, coffee, or tea are thickened with an added thickening agent prior to being fed to a dysphagic subject. However, there has not been implemented any objective set of criteria to define the levels of thickness/viscosity which constitute a nectar thick composition versus a honey thick composition. The health provider simply thickens the desired food to a subjective thickness and provides it to the patient. This lack of standardization fosters great variability in practice. In short, individual speech pathologists, dieticians, food service managers, and food manufacturers arbitrarily determine, based upon their own subjective evaluation, what constitutes a nectar thick composition and a honey thick composition. In the vast majority of instances, no objective measurement of the increased viscosity of the modified food is taken. If a measurement is taken, it is done using rough, empirical evaluations of viscosity, such as the Line Spreading Test (LST), a test developed in the 1940s to gauge the consistency of foods. See Grawemeyer, E. A. and Pfund, M. C. (1943) Line spread as an objective test of consistency,” Food Research 8:105-108. This greatly hinders gathering detailed information on the efficacy of using thickened liquids in the treatment of dysphagia.
Dysphagia is associated with increased mortality and morbidity, including malnutrition, dehydration, pulmonary complications, and reductions in quality of life. These sequelae cost millions of healthcare dollars in hospitalizations, outpatient visits and increased need for supported care. It is estimated that over 18 million adults and millions of children in the United States are dysphagic. As noted above, people suffering from dysphagia are diagnosed radiographically using standardized barium fluids. One common treatment strategy identified from the diagnostic evaluation is the need for patients to drink thickened liquids to prevent misdirection of fluids into the airway. The commercially available diagnostic fluids (available from providers such as Bracco Diagnostics, Inc., Princeton, N.J. USA and Bracco Imaging SpA, Milan, Italy) are characterized by an apparent viscosity at 30 s−1 as nectar (˜300 cP), thin honey (˜1,500 cP) or honey (˜3,000 cP). Apparent viscosity is the standard measure against which thickened fluids are typically measured. However, commercially-available thickened beverages, which are supposedly based on the standards of viscosity set by the diagnostic fluids, vary greatly from the apparent viscosity of the commercially available diagnostic fluids.
Therefore, there continues to be a long-felt and unmet need in the study and treatment of dysphagia for a standardized set of edible compositions for both the gross evaluation of dysphagia and for a corresponding viscosity-standardized set of edible compositions, either with a radio-opaque agent for use in the radiographic imaging of the mouth and throat, or without a radio-opaque agent for providing satisfying sustenance to dysphagic individuals.